1. Field of the Invention
The invention relates to ink jet printing, and, more particularly, to multiple jet ink jet printing.
2. Description of the Prior Art
Ink jet printers having an insufficient number of ink jets to span the entire width of a document to be printed, may recirculate the document on a rotary drum, while moving the ink jets axially of the drum. After the document has been printed, the document is unloaded, a new document loaded, and the ink jets are moved back to the initial position.
The slow, precision mechanism for moving the ink jets while printing is unsuitable for moving the ink jets back to the initial position at high speed. Hence, a special high-speed flyback mechanism must be provided, and means must be provided for precisely positioning the ink jets at the initial position.
In such precision printing systems, the drum rotation and the data transmission capabilities are unidirectional. Thus, the drum direction and ink jet print direction cannot be reversed to print alternate documents. Drums are unidirectional primarily because the document loading and unloading mechanisms are usable only while the drum is rotating in a single direction, and because the time required to stop a drum and reverse its direction would be so high as to be impractical.
An early patent, U.S. Pat. No. 1,736,219, Ranger, issued Nov. 19, 1929, "Cross Screen Picture Receiving System" discloses printing a single document by scanning a single hot air print element back and forth while the document is rotated by a drum. It requires, however, a data source or scanner which also moves back and forth and transmits the data in the same fashion as used. Such a system is extremely slow in that each point is printed twice and is not precise. Nothing is proposed for multiple print elements.
U.S. Pat. No. 3,764,994, Brooks et al, issued Oct. 9, 1973, "Serial Printer with Bi-Directional Drive Control" teaches a printer having a moving print mechanism which scans first in one direction across a stationary document to print a line of characters, steps the document to the next line, and scans in the reverse direction to print the next line. The stepping function is not sufficiently precise to allow high quality printing of images, and the bidirectional arrangement cannot be used with a continuously rotating precision drum.
It is therefore an object of the present invention to provide apparatus for producing high quality printing with multiple jet ink jets without moving the ink jets back across a document to the same initial position after printing.